At the time of producing a fluorinated polymer such as a polytetrafluoroethylene (hereinafter referred to as PTFE), a melt-processable fluororesin or a fluoroelastomer by emulsion polymerization, it is common to use an anionic fluorinated emulsifier in order not to hinder the polymerization reaction by chain transfer in an aqueous medium.
An aqueous emulsion of a fluorinated polymer (hereinafter referred to as a fluorinated polymer aqueous emulsion) obtained by emulsion polymerization is subjected to coagulation, followed by drying, to obtain a powder of the fluorinated polymer. A powder of a fluorinated polymer, particularly a fine powder of PTFE, is molded by a method such as paste extrusion molding and then, used for various applications. Otherwise, if necessary, a nonionic surfactant, etc. may be added to a fluorinated polymer aqueous emulsion for stabilization treatment, followed by concentration treatment to obtain a fluorinated polymer aqueous dispersion containing the fluorinated polymer at a high concentration. Such a fluorinated polymer aqueous dispersion may be used, if necessary, by an addition of various compounding ingredients, for various coating applications, impregnation applications, etc.
On the other hand, an anionic fluorinated emulsifier to be used for emulsion polymerization of a fluorinated polymer is not easily decomposed in the natural world. Therefore, in recent years, it is desired to reduce an anionic fluorinated emulsifier contained not only in industrial effluents but also in products such as a fluorinated polymer aqueous emulsion, a fluorinated polymer aqueous dispersion, etc.
As a method for reducing an anionic fluorinated emulsifier, there is a method wherein a liquid to be treated, such as an aqueous emulsion or an aqueous dispersion, containing an anionic fluorinated emulsifier, is contacted to a basic ion exchange resin, so that the anionic fluorinated emulsifier in the liquid to be treated is adsorbed on the basic ion exchange resin. Further, since the anionic fluorinated emulsifier is expensive, it has been attempted to recover and reuse the anionic fluorinated emulsifier adsorbed on the basic ion exchange resin.
For example, Patent Document 1 discloses a method of treating a basic ion exchange resin having an anionic fluorinated emulsifier adsorbed thereon, with a mixture of a dilute mineral acid and an organic solvent, to recover the emulsifier as an acid of the anionic fluorinated emulsifier. It is disclosed that the organic solvent is preferably a solvent which is miscible with water to present a solubility of at least 40% or which can be unlimitedly mixed with water, and an alcohol such as methanol, a cyclic ether such as dioxane, methylene chloride, etc. may be used.
Further, Patent Document 2 discloses a method wherein by means of an inorganic acid and a water-insoluble fluorinated medium, from a basic ion exchange resin having an anionic fluorinated emulsifier adsorbed thereon, an acid of the anionic fluorinated emulsifier is eluted in the water-insoluble fluorinated medium for recovery.